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Title: A nucleosynthetic origin for the Earth’s anomalous 142Nd composition

Abstract

A long-standing paradigm assumes that the chemical and isotopic compositions of many elements in the bulk silicate Earth are the same as in chondrites(1-4). But, the accessible Earth has a greater Nd-142/Nd-144 ratio than do chondrites. Because Nd-142 is the decay product of the now-extinct Sm-146 (which has a half-life of 103 million years(5)), this Nd-142 difference seems to require a higher-than-chondritic Sm/Nd ratio for the accessible Earth. This must have been acquired during global silicate differentiation within the first 30 million years of Solar System formation(6) and implies the formation of a complementary Nd-142-depleted reservoir that either is hidden in the deep Earth(6), or lost to space by impact erosion(3,7). Whether this complementary reservoir existed, and whether or not it has been lost from Earth, is a matter of debate(3,8,9), and has implications for determining the bulk composition of Earth, its heat content and structure, as well as for constraining the modes and timescales of its geodynamical evolution(3,7,9,10). We show that, compared with chondrites, Earth's precursor bodies were enriched in neodymium that was produced by the slow neutron capture process (s-process) of nucleosynthesis. This s-process excess leads to higher Nd-142/Nd-144 ratios; after correction for this effect, the Nd-142/Nd-144 ratiosmore » of chondrites and the accessible Earth are indistinguishable within five parts per million. The Nd-142 offset between the accessible silicate Earth and chondrites therefore reflects a higher proportion of s-process neodymium in the Earth, and not early differentiation processes. Our results obviate the need for hidden-reservoir or super-chondritic Earth models and imply a chondritic Sm/Nd ratio for the bulk Earth. Although chondrites formed at greater heliocentric distances and contain a different mix of presolar components than Earth, they nevertheless are suitable proxies for Earth's bulk chemical composition.« less

Authors:
 [1];  [2];  [3];  [3];  [4];  [5]
  1. Univ. of Chicago, IL (United States). Dept. of Geophysical Sciences and Enrico Fermi Inst.; Munster Univ. (Germany). Inst. for Planetology
  2. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  3. Munster Univ. (Germany). Inst. for Planetology; Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  4. Univ. of Chicago, IL (United States). Dept. of Geophysical Sciences and Enrico Fermi Inst.
  5. Munster Univ. (Germany). Inst. for Planetology
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1395508
Report Number(s):
LLNL-JRNL-689320
Journal ID: ISSN 0028-0836; nature18956
Grant/Contract Number:
AC52-07NA27344
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Nature (London)
Additional Journal Information:
Journal Name: Nature (London); Journal Volume: 537; Journal Issue: 7620; Journal ID: ISSN 0028-0836
Publisher:
Nature Publishing Group
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; 58 GEOSCIENCES; geochemistry; geodynamics; early solar system; SOLAR PROTOPLANETARY DISK; HETEROGENEOUS DISTRIBUTION; ISOTOPIC HETEROGENEITY; ENSTATITE CHONDRITES; BULK COMPOSITION; HALF-LIFE; NEBULA; SYSTEMATICS; ND; DIFFERENTIATION

Citation Formats

Burkhardt, C., Borg, L. E., Brennecka, G. A., Shollenberger, Q. R., Dauphas, N., and Kleine, T.. A nucleosynthetic origin for the Earth’s anomalous 142Nd composition. United States: N. p., 2016. Web. doi:10.1038/nature18956.
Burkhardt, C., Borg, L. E., Brennecka, G. A., Shollenberger, Q. R., Dauphas, N., & Kleine, T.. A nucleosynthetic origin for the Earth’s anomalous 142Nd composition. United States. doi:10.1038/nature18956.
Burkhardt, C., Borg, L. E., Brennecka, G. A., Shollenberger, Q. R., Dauphas, N., and Kleine, T.. 2016. "A nucleosynthetic origin for the Earth’s anomalous 142Nd composition". United States. doi:10.1038/nature18956. https://www.osti.gov/servlets/purl/1395508.
@article{osti_1395508,
title = {A nucleosynthetic origin for the Earth’s anomalous 142Nd composition},
author = {Burkhardt, C. and Borg, L. E. and Brennecka, G. A. and Shollenberger, Q. R. and Dauphas, N. and Kleine, T.},
abstractNote = {A long-standing paradigm assumes that the chemical and isotopic compositions of many elements in the bulk silicate Earth are the same as in chondrites(1-4). But, the accessible Earth has a greater Nd-142/Nd-144 ratio than do chondrites. Because Nd-142 is the decay product of the now-extinct Sm-146 (which has a half-life of 103 million years(5)), this Nd-142 difference seems to require a higher-than-chondritic Sm/Nd ratio for the accessible Earth. This must have been acquired during global silicate differentiation within the first 30 million years of Solar System formation(6) and implies the formation of a complementary Nd-142-depleted reservoir that either is hidden in the deep Earth(6), or lost to space by impact erosion(3,7). Whether this complementary reservoir existed, and whether or not it has been lost from Earth, is a matter of debate(3,8,9), and has implications for determining the bulk composition of Earth, its heat content and structure, as well as for constraining the modes and timescales of its geodynamical evolution(3,7,9,10). We show that, compared with chondrites, Earth's precursor bodies were enriched in neodymium that was produced by the slow neutron capture process (s-process) of nucleosynthesis. This s-process excess leads to higher Nd-142/Nd-144 ratios; after correction for this effect, the Nd-142/Nd-144 ratios of chondrites and the accessible Earth are indistinguishable within five parts per million. The Nd-142 offset between the accessible silicate Earth and chondrites therefore reflects a higher proportion of s-process neodymium in the Earth, and not early differentiation processes. Our results obviate the need for hidden-reservoir or super-chondritic Earth models and imply a chondritic Sm/Nd ratio for the bulk Earth. Although chondrites formed at greater heliocentric distances and contain a different mix of presolar components than Earth, they nevertheless are suitable proxies for Earth's bulk chemical composition.},
doi = {10.1038/nature18956},
journal = {Nature (London)},
number = 7620,
volume = 537,
place = {United States},
year = 2016,
month = 9
}

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